C++统计字符频数_英文字符

//data.txt需要放在相同目录下
//只能计算纯英文文件中的字符.
#include <iostream>
#include <map>
#include <fstream>
#include <algorithm>
#include <string>
#include <ctime>
#include <iomanip>

using namespace std;

int main(){
	ifstream infile("data.txt");
	string s1;
	char c;
	map<char,int> m1;
	multimap<double,char> m2;
	int sumchar=0;
	
	clock_t start,end;

	start=clock();
	while(infile.get(c)){
		m1[c]++;
		sumchar++;
	}
	
	std::map<char,int>::iterator it1=m1.begin();
	for(;it1 != m1.end(); it1++){
		m2.insert(pair<double,char>((it1->second*1.0/sumchar),it1->first));
	}
	
	end=clock();

	cout<<"共计:"<<(end-start)/1000<<"毫秒"<<endl;
	//cout<<(end-start)/CLOCKS_PER_SEC<<"秒"<<endl;
	cout<<"总计:"<<sumchar<<"个字符"<<endl<<endl;
	
	
	std::multimap<double,char>::iterator it2=m2.begin();
	for(;it2 != m2.end();it2++){
		cout<<it2->second<<" "
			<<setw(4)<<it2->first*100<<"%"
			<<endl;
	}
}